Overview

This Robotic Arm Claw kit is an Arduino based system which comes with 4 degrees of freedom. This project aims to interface an Arduino Uno with a 16 channel PWM/Servo shield and using potentiometer to control the Robotic arm movements. The shield uses I2C Communication.

Hardware Used

• Arduino

4DOF Robotic Arm Claw Kit

5V Power Supply

Breadboard

Jumper Wires

16 x 12-bit PWM/Servo shield

4-pcs Potentiometers 

Software Used

• Arduino IDE

Library used

• Adafruit_PWMServoDriver.h
• Wire.h

Hardware Set-up

We are using the 16 channel 12-bits PWM servo shield.

The 16-Channel 12-bit PWM/Servo Driver Shield will drive up to 16 servos over I2C with only 2 pins. The on-board PWM controller will drive all 16 channels simultaneously with no additional Arduino processing overhead.

Up to 16 servos can be attached to one board. If you need to control more than 16 servos, additional boards can be stacked.

What is PWM?

Pulse Width Modulation, or PWM, is a technique for getting analog results with digital means. Digital control is used to create a square wave, a signal switched between on and off. This on-off pattern can simulate voltages in between full on (5 Volts) and off (0 Volts) by changing the portion of the time the signal is in the ON state versus the time that the signal is in the OFF state. The duration of “ON time” is called the pulse width. To get varying analog values, you change, or modulate, the pulse width.

 

Here are the steps on how to assemble your Robotic arm kit:

 

 

 

 

 

 

 

 

 

 

NOTE:
Make sure that the screws are not over tightened so that the joints can move freely and the holes of the joints will not worn out.

Schematic Diagram

Code

#include <Adafruit_PWMServoDriver.h>
#include <Wire.h>
#define SERVOMIN 150 // this is the 'minimum' pulse length count (out of 4096)
#define SERVOMAX 600 // this is the 'maximum' pulse length count (out of 4096)

// called this way, it uses the default address 0x40
Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver();
// you can also call it with a different address you want
//Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver(0x41);
// you can also call it with a different address and I2C interface
//Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver(&Wire, 0x40);

// Depending on your servo make, the pulse width min and max may vary, you 
// want these to be as small/large as possible without hitting the hard stop
// for max range. You'll have to tweak them as necessary to match the servos you

uint8_t servo1 = 0, servo2 = 1, servo3 = 2, servo4 = 3; // Servo pin number
int potpin1 = A0,potpin2 = A1,potpin3 = A2,potpin4 = A3; // analog pin used to connect the potentiometer
int val1,val2,val3,val4; // variable to read the value from the analog pin

void setup() {
   Serial.begin(9600);

  pwm.begin();
  
  pwm.setPWMFreq(60);  // Analog servos run at ~60 Hz updates

  delay(10);
  

}

void loop() {

 val1 = analogRead(potpin1);
 val1 = map(val1,0,1023,SERVOMIN,SERVOMAX);
 pwm.setPWM(servo1,0,val1);
 Serial.println(val1);
 delay(15);
 
 val2 = analogRead(potpin2);
 val2 = map(val2,0,1023,SERVOMIN,SERVOMAX);
 pwm.setPWM(servo2,0,val2);
 Serial.println(val2);
 delay(15);
 
 val3 = analogRead(potpin3);
 val3 = map(val3,0,1023,SERVOMIN,SERVOMAX);
 pwm.setPWM(servo3,0,val3);
 Serial.println(val3);
 delay(15);
 
 val4 = analogRead(potpin4);
 val4 = map(val4,0,1023,SERVOMIN,SERVOMAX);
 pwm.setPWM(servo4,0,val4);
 Serial.println(val4);
 delay(15);
 
}

This is the code for the entire system.

#include <Wire.h>
#include <Adafruit_PWMServoDriver.h>

// called this way, it uses the default address 0x40
Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver();

This calls the library for I2C which is the Wire.h and for the PWM servo driver which is  Adafruit_PWMServoDriver.h.

void setup() {
   Serial.begin(9600);

  pwm.begin(); //this is to begin pwm
  
  pwm.setPWMFreq(60);  // Analog servos run at ~60 Hz updates

  delay(10);

This function can be used to adjust the PWM frequency, which determines how many full ‘pulses’ per second are generated by the IC.

 

val1 = analogRead(potpin1);  // reads the value of the potentiometer (value between 0 and 1023)

 val1 = map(val1,0,1023,SERVOMIN,SERVOMAX); // scale it to use it with the servo (value between 0 and 180)
 pwm.setPWM(servo1,0,val1);
 Serial.println(val1);
 delay(15);

The setPWM function sets the start (transition from OFF to ON) and end (transition from ON to OFF) of the HIGH state of the PWM pulse on a specific channel.  You specify the ‘tick’ value between 0 to 4095 when the signal will turn on, and when it will turn off.  servo1 indicates which of the 16 PWM outputs should be updated with the new values.

Conclusion

The system is not limited to what is described above as it only illustrates basic functionality using analog input. You can always change and improve with your desired output. You can even add additional sensors or wireless/remote control to make the robotic arm kit even more interesting.

References

• https://learn.adafruit.com/adafruit-16-channel-pwm-slash-servo-shield/overviewh
• https://github.com/adafruit/Adafruit-PWM-Servo-Driver-Library
• https://www.auselectronicsdirect.com.au/assets/files/TA0262%20Instruction%20Manual%20revised.pdf
• https://www.arduino.cc/en/Tutorial/PWM

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